Running back James Conner has been ruled out of the Pittsburgh Steelers' road game against the Oakland Raiders, coach Mike Tomlin announced Tuesday.

Tomlin described Conner's injury as a sprain, not as a contusion as initially thought. He did not indicate whether the injury will keep the second-year running back sidelined for more than one week.

The Steelers added depth to their backfield on Tuesday by signing running back Trey Edmunds to the active roster.

Wide receiver Justin Hunter was placed on injured reserve to open the roster spot for Edmunds, who will join rookie Jaylen Samuels and veteran Stevan Ridley in the backfield.

Tomlin said he expects to employ a running-back-by-committee approach versus Oakland.

"That is our intention as we sit here," Tomlin said.

Conner sustained an ankle injury in Sunday's 33-30 setback to the Los Angeles Chargers on Sunday night. He was injured after being tackled following a reception on a screen pass with 5:08 remaining in the fourth quarter.

The 23-year-old Conner rushed for 60 yards and two touchdowns against the Chargers. He added three receptions for 14 yards for the Steelers (7-4-1), who will visit Raiders (2-10) on Sunday (4:25 p.m. ET).

Conner has 201 carries for 909 yards and 12 touchdowns in 12 games this season. The 6-foot-1, 233-pound Conner also has 52 receptions for 467 yards and one score.

Samuels, 22, has rushed for 31 yards on 12 carries since being selected by Pittsburgh in the fifth round of the 2018 NFL Draft. The 6-foot, 225-pound North Carolina State product also has seven catches for 54 yards and two scores.

Edmunds was on the practice squad since the start of the season. He is the older brother of safety Terrell Edmunds, the team's first-round pick in April.

The older Edmunds initially was signed by the New Orleans Saints in 2017 as an undrafted rookie free agent from Maryland. He had nine carries for 48 yards and a touchdown in 16 regular-season games.

Hunter sustained a shoulder injury on Sunday, ending his season with three receptions for 21 yards.

The Steelers also signed linebacker Matthew Thomas to the practice squad. Thomas, who originally signed by Pittsburgh as an undrafted rookie free agent from Florida State this year, played in 10 games this season.